luminosity

Different brightnesses of objects affect the speed at which we see things. That might seem odd. Everything we see is reflecting light and light goes at, well, the speed of light. We could also look at a light and that would be, well, the speed of light again. I’ll try not to use any of the big words that I barely understood from optometry school but you can load up on that using google (bing?). Have fun with these words if you want, luminosity (luminance) and illuminance. Our perception of various intensities of light from bright to dim objects affect how fast our brain thinks something might be moving.

Here’s a simple test that you can do to demonstrate this. Don’t get mad at me if you don’t get the effect easily but it does work. At the end of this post here you can watch a youtube video to see how they did the experiment. It’s frequently used in the real world as well so this isn’t some hokey thing. Also, 3D effects can be done using this method. Tie a string around an object, something maybe the size of a small ball or tennis ball (doesn’t have to be a round object though). Cover one eye with a dark lens like a dark sunglasses lens and make sure your other eye isn’t looking through anything other than a clear lens or nothing at all. Have someone swing the tennis ball back in forth in front of you like they are trying to play the hypnotist. Not back and forth so it hits you in the nose. Swing it the other way (and not in a circular pattern please). Apparently some may notice the effect more than others. The swinging object hopefully looks like it’s going in an elliptical pattern (sorta circular). What does that mean? Before you read the next paragraph, the effect is normal!

I’m not going to say that anyone has an eye disease if they notice the effect more than the other person, but, there are medical conditions that have shown that this phenomenon can occur without the sunglasses lens. It’s called the Pulfrich Effect whether you do it with the lens or not. The effect can be demonstrated in unilateral optic neuritis. That’s code for multiple sclerosis. Other times this phenomenon might indicate a color abnormality in one eye or an amblyopic person who has poor vision in one eye. A unilateral cataract might also elicit the effect. I don’t believe I know any eye doctor that performs this as a test in their office to help in diagnosing any of these conditions though. This kind of test lends itself more to research studies.

Why does this effect occur you ask? It has something to do with the luminance of the object and how our neural system interprets that. Our brain has a funny way of getting us to see certain things in the visual world in a strange way based on the brightness or dimness of an object. You’ve probably seen plenty of those visual illusions where things in a picture seems to be rotating or moving. I’ll probably do another post or more on some of those phenomenon.